PARIS — The diamond show was staged on the ground floor of a hotel that thieves had targeted before — and which, in fact, had featured in Alfred Hitchcock's high-karat classic "To Catch a Thief." The guards were few and unarmed, and nobody thought to tell the police about the tens of millions of dollars worth of gems on display for more than a month.

On Tuesday, questions arose about how the collection was left so vulnerable that a single thief with a handgun managed to make off over the weekend with one of the biggest hauls in history — a total of $136 million in jewels — without firing a shot.

It was the second time in a week that unarmed guards were overwhelmed by jewel thieves. At a Swiss prison near the French border, a member of the notorious "Pink Panther" gang escaped after accomplices rammed a gate and overpowered unarmed guards with bursts from Kalashnikovs.

Private security guards are generally prohibited from carrying weapons in France and Switzerland — that's reserved for police — but special authorizations can be granted when high-value assets are at stake.

"It can't be standard procedure when you have that kind of value. This is an extraordinary amount of value to have in one place from one company," said John Kennedy, president of the New York-based Jewelers Security Alliance. In the United States "those shows are limited to the trade. You have to have an ID and have a pass. It's not open to the public."

With the measures in place, he said, it was nearly irrelevant whether the heist at the Carlton Intercontinental Hotel in Cannes was an inside job.

"What do you need with an inside job when a guy can walk in and do this? What inside information do you need — there's a big diamond show," he said. Cannes' storied history of jewel heists apparently made little difference to those planning the show, he said, adding that U.S. insurers he'd spoken with had found the entire escapade bizarre.

"In the United States there are certain hotels that don't want jewelry shows at all because they're dangerous," he said. "If you couldn't have it with armed guards I'd say you have a serious, serious problem."

That's not a view widely held on the other side of the Atlantic.

"The public carrying of weapons — even by security guards and police officers — is much less visible throughout Europe than it is in parts of North America," said Keith Krause, program director of the Geneva-based Small Arms Survey, a nonprofit that monitors global views of weapons.

"Given that civilian possession of weapons is much less available, they're unlikely to have weapons because they're unlikely to be facing people with weapons."

Zakaria Rami, a union representative at the Carlton who has worked there for 16 years, said show organizers didn't formally advise police of the show. Only a few guards hired by the jeweler provided security in a hotel showroom site where the robber struck on Sunday.

"If police knew there was $100 million in jewelry, I think they would have put a patrol car out there," he said.

The show was far from inconspicuous: One-story tall, bright pink banners covered the front facade of the Carlton, one of the most famous hotels on La Croisette — Cannes' best-known seaside promenade.

Rami wasn't at the Carlton in 1994 when a gunman opened fire at the hotel, injuring a guard before making off with $45 million in jewels. That robbery prompted the city to suspend the gem shows that draw jewelers to the French Riviera each summer, hoping to catch the eye of travelers with money to burn. The ban expired years ago, and the shows resumed.

The jewels on display routinely catch some unwanted attention. Rami said he can think of four or five other major robberies in his time in Cannes, which appears to be a favorite target this year. In May it was struck by other two highly publicized heists during the Cannes Film Festival.

"For security in a hotel that was housing such a collection, it's more a question that can be asked of the victim — and its insurer — than of police services," said Cmdr. Bernard Mascarelli, head of the judicial police in nearby Nice, whose Bureau for the Repression of Banditry is leading the investigation.

The owner of the collection, Israeli billionaire Lev Leviev, has said little about the theft, but noted in a statement Tuesday that the company was working with police and insurers.

"Leviev takes the security of our staff and merchandise very seriously and all reasonable security measures required by our insurers were implemented prior to the robbery taking place," the statement said.

Philippe Vique, an assistant prosecutor in the Riviera town of Grasse, said there was no break-in at the hotel, and the private security guards were not armed. The gunman went in through French doors and exited less than a minute after the holdup, he said. Rami, the union official, said the suspect was not pursued.

Alain Bauer, a leading French criminologist and security expert, said the show's organizer "could have called on the police — that in this specific case would have put armed officers in place."

Bauer, who is currently teaching in Colorado, acknowledged there is a different mindset about the right to bear arms in the European Union and in the United States.

"Between losing several millions of euros and killing someone, Europeans' choice has been that we'd rather lose several million euros," he said by telephone. "The idea that having more firearms creates more security isn't convincing in Europe."

"In this case, it's more a question of disorganization than of weapons," he said.

Police in Cannes haven't drawn any specific links between Cannes and the escape Thursday of Milan Poparic, said to be the third member of the Pink Panther group to break out of a Swiss prison in as many months.

"But the Pink Panthers are known for these brazen acts of rushing into a place, quickly intimidating the people there and getting the loot and making their getaway," said Scott Andrew Selby, co-author of "Flawless: Inside the Largest Diamond Heist in History," about a 2003 heist in Antwerp, Belgium.

For the thieves, France is a place "they're comfortable hitting."

Selby said it's unlikely the bandit was working alone — suggesting he might have had a "scout" to scope out the hotel beforehand, or a getaway driver at the ready, even an adviser to help fence the stolen diamonds later on.

French authorities were poring over video surveillance footage, going back over other jewelry-theft case files and conducting other "standard judicial police work," said Mascarelli by phone.

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